Magnetic proximity switches are used in many and varied operational environments to provide a changing electrical signal depending on the proximity of some target to the switch. Magnetic proximity switches may be used in an almost infinite number of different applications. In one common application, for example, a magnetic proximity switch may be used in conjunction with a valve to sense when the valve is in an open or closed position.
One typical magnetic proximity switch includes, in a very basic arrangement, a common electrical contact that is movable between two different contacts to complete either a first circuit or a second circuit. The common contact is attached to or includes a ferrous or magnetic sensing member that will shift in a first direction when a target, such as another magnet or ferrous structure, approaches within a certain distance, or sensing range, of the sensing member. Typically, the sensing member and/or the common contact is also biased to shift in an opposite, second direction when the target retreats away from the sensing member beyond the sensing range.
Proximity switches are often used in very harsh operating environments, such as under water and in dirty environments in which abrasives, such as dirt, metal shavings, and/or caustic chemicals, are present. A few exemplary harsh operating environments include, without limitation, deep sea oil and gas extraction, chemical and petrochemical refineries, heavy industrial plants such as steel mills and heavy manufacturing and machining operations, sandy desert environments, and so on.
In addition, proximity switches are often used in environments where fail-safe operation is of a top priority, such as in nuclear power generation plants, and in which any equipment used in such environments must meet elevated operating specification in order to prevent malfunctioning under even extreme operating conditions. In nuclear applications, for example, some such specifications are intended to prevent malfunctioning of components under elevated seismic acceleration loading.